1. Technical Field
The present invention relates to an optical position measuring arrangement suitable for determining the relative position of two objects, which are movable in relation to each other, and provides a reference pulse signal at least one reference position along the measuring track.
2. Background Information
For determining the relative position of two objects which are movable in relation to each other, known incremental position measuring arrangements contain an incremental graduation track as a part of a scale. For generating incremental signals, the incremental graduation track is scanned by a scanning unit, which is movable in at least one measuring direction. Moreover, for providing an absolute relationship, such position measuring arrangements have the possibility of generating reference pulse signals at defined, or respectively predetermined reference positions along the measuring track. For this purpose a further track is arranged at one or several predetermined reference positions on the part of the scale, for example adjoining the incremental graduation track. The reference markings customarily include a plurality of graduated areas, which are a periodically arranged in the measuring direction and have different optical properties. In the case of incident light scanning, these are perhaps graduated areas of different reflectivity, in the case of transmitted light scanning the graduated areas are of different transparency.
The scanning unit which, with respect to the scale, is movable in the measuring direction, is connected with the respectively other object and includes a light source, a reference pulse detector arrangement, as well as further components, as required, for incremental signal generation, however, the latter are of no further importance in the present connection. The reference pulse detector arrangement includes individual opto-electronic detector elements, whose geometric arrangement is matched to the reference markings for generating a reference pulse signal. Customarily, the reference pulse detector arrangement here has the same structure as the reference marking.
When passing over the reference marking, a signal maximum of the reference pulse now results in such a position measuring arrangement at the respective reference position. More or less pronounced secondary maxima of the reference pulse signal exist in the areas adjacent to the reference position. In the case of particularly strongly pronounced secondary maxima, a certain uncertainty regarding the detection of the actual signal maximum at the reference position exists because of the reduced interference spacing between a base signal level and the signal maximum.
For solving this problem it has already been proposed in U.S. Pat. No. 4,451,731, the entire contents of which are incorporated herein by reference, or respectively in DE 20 2005 002 622 U1, to provide further structural elements, or respectively additional structural elements, on the scale adjacent to the actual reference marking for repressing secondary maxima in the resulting reference pulse signal. Here, the additional structures employed for this includes non-reflective or opaque lines adjacent to the reference marking which, in certain scanning configurations, assure damping of the secondary maxima of the reference pulse signal.